In many response measurements, a high-power pulse or series of pulses having a well-defined frequency is applied to a material sample and the sample response is then measured at that specific frequency after the pulses have been turned off, using a detector which resonates at the same frequency.
In the technique of stochastic nuclear magnetic resonance (NMR), which was invented many years ago, a random or pseudorandom (stochastic) radio frequency signal or pulse stream is applied to a sample and the sample response is detected by a high-Q input circuit, tuned to the specific frequency of interest and connected to a high sensitivity detection amplifier. Such detection systems achieved their sensitivity by using a high-Q detection circuit which has a bandwidth, B, limited by the nature of the high-Q circuit, and determined from the equation: ##EQU1## In these detection systems, the sample is driven with a very wide range of frequencies in the stochastic excitation signal but the detection system operates with high sensitivity only within the relatively narrow bandwidth, B, determined by the Q of the input circuit. In addition, when this type of detection system is exposed to the stochastic excitation signal, the input amplifier usually saturates, so the normal implementation uses a series of stochastic pulses (having random amplitudes and phases) to excite the sample, and the detection system is used to measure the sample response between the pulses.